Power switch drive circuit and device

ABSTRACT

The invention relates to the field of power semiconductor devices. This invention discloses a drive circuit and device of a power switch. The input terminal of the drive circuit receives a pulse signal; the output terminal of the drive circuit is connected to a capacitor circuit. The capacitor circuit is used to provide a negative voltage for a first electrode of the power switch to turn off the power switch when the pulse signal is a turn-off signal; the drive circuit includes a capacitance adjustment unit. The capacitance adjustment unit includes a negative voltage adjustment element that can charge a capacitor whose voltage is lower than a predetermined voltage when the pulse signal is the turn-off signal.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation application of InternationalApplication No. PCT/CN2019/070648, filed on Jan. 7, 2019, which claimspriority to Chinese Patent Application No. CN201810896181.9, filed onAug. 8, 2018. The disclosures of the aforementioned applications arehereby incorporated herein by reference in their entireties.

TECHNICAL FIELD

The invention relates to the field of power semiconductor devices, inparticular to a drive circuit and device of a power switch.

BACKGROUND

Power semiconductor drive circuits are mainly used for driving powersemiconductor switching devices such as devices formed of siliconcarbide, silicon, gallium nitride, etc. Power semiconductor drivecircuits are widely used in the design of power converters. These powerconverters include AC/DC converters, DC/DC converters, and DC/ACconverters. Terminal equipment that uses these power converters includespower supplies, motor drive equipment, solar energy conversionequipment, new energy vehicles, etc.

The structures of the existing drive circuits are shown in FIGS.1(a)-(c). Among them, the drive circuit including field effecttransistors (MOS) Q1 and Q2 receives an input pulse signal. After powerand level amplification, the drive circuit generates a drive signal forcontrolling the on and off of the power switch Q3. Cn is a capacitor. Rgand Rc are Resistors. Dc is a diode. Dz is a Zener diode. VDD is a powersupply voltage.

The circuit shown in FIG. 1(a) is the simplest solution to provide anegative voltage for the gate drive voltage Vg of Q3 when a turn-offsignal is received. However, when the Pulse Width Modulation (PWM)signal is activated, the initial storage voltage of the capacitor (Cn)may be zero or lower than a predetermined voltage after the voltage ofthe capacitor has been discharged. In a certain period of time after thesignal has been activated, this will cause the positive gate voltage tobe too high, and the negative gate voltage to be insufficient (as shownin FIG. 2). Moreover, in this circuit, the capacitor can be charged onlywhen the PWM signal (e.g., pulse signals) is a high-level signal. If thePWM signal (e.g., pulse signals) is in a low-level state (such as anidle state) for a long time, the capacitor cannot be replenished intime. The voltage of the capacitor may drop due to leakage or otherinterference factors. This may result in insufficient negative voltageon the gate, which is unable to maintain a reliable shutdown of thepower switch before the power switch is switched on again, thus causingreliability issues of the power switch and its associated drive circuit.Especially for silicon carbide Metal-Oxide-Semiconductor Field-EffectTransistor (SiC MOSFET), it usually has a narrow positive gate voltagerange and a lower gate threshold voltage.

The drive circuit shown in FIG. 1(b) uses an external simple circuitcomprising Cn and Dz to generate a negative voltage. This circuit solvesthe startup problem in FIG. 1(a). However, this circuit requires aseparate isolated bias voltage (e.g., voltage source +V). In thiscircuit, the simple bootstrap circuit cannot be used to power thehigh-side drive circuit of a half-bridge, which will add greatcomplexity to the system, thereby increasing the cost of the circuit.

The drive circuit shown in FIG. 1(c) simplifies the entire circuit, butthe circuit requires two isolated bias voltages (+V and −V) havingpositive and negative voltages to generate the negative bias required bythe power switch. The isolated bias voltages can add a lot of complexityto the system.

Therefore, there is an urgent need to provide a simple, reliable, lowpin count, but fully functional IC integrated circuit solution torealize the gate drive function of the power switch device.

SUMMARY OF THE INVENTION

The object of the present invention is to provide a drive circuit for apower switch. This drive circuit can maintain the capacitor voltage whenthe pulse signal is off for a long time. The drive circuit can provide astable negative voltage for the power switch to maintain the turn off ofthe power switch.

In order to solve the technical problems above, the embodiments of thepresent invention disclose a drive circuit for a power switch. The inputterminal of the drive circuit receives a pulse signal. The pulse signalincludes a turn-on signal for controlling the power switch to be turnedon and a turn-off signal for controlling the power switch to be turnedoff. The output terminal of the drive circuit is connected to acapacitor circuit. The capacitor circuit is used to provide a negativevoltage for a first electrode of the power switch to turn off the powerswitch when the pulse signal is a turn-off signal;

The drive circuit includes a capacitance adjustment unit. Thecapacitance adjustment unit includes a negative voltage adjustmentelement that can charge a capacitor whose voltage is lower than apredetermined voltage when the pulse signal is the turn-off signal. Thecapacitor is included in the capacitor circuit.

In an exemplary embodiment, the negative voltage adjustment elementincludes a negative voltage charge pump, which is used to charge thecapacitor whose voltage is lower than the predetermined voltage when thedrive circuit receives the turn-off signal.

In an exemplary embodiment, the negative voltage charge pump isconnected in parallel with the capacitor circuit, and the low voltageend of the capacitor is connected to the first electrode of the powerswitch.

In an exemplary embodiment, the capacitance adjusting unit furtherincludes a positive voltage adjustment element, which is used to chargethe capacitor whose voltage is lower than a predetermined voltage whenthe drive circuit receives a turn-on signal.

In an exemplary embodiment, the positive voltage adjustment elementincludes a first resistor and a diode connected in series;

The first terminal of the first resistor is connected to the low voltageend of the capacitor. The second terminal of the first resistor isconnected to the anode of the diode. The cathode of the diode isconnected to ground.

In an exemplary embodiment, the capacitance adjustment unit furtherincludes an over-voltage adjustment element for clamping the voltage ofthe capacitor to a predetermined voltage when the voltage of thecapacitor exceeds the predetermined voltage.

In an exemplary embodiment, the drive circuit further includes acharging unit for charging the capacitor with a current source in thecharging unit when the drive circuit is started, and,

When the charging unit charges the capacitor, the low voltage end of thecapacitor and a second electrode of the power switch are both grounded.

In an exemplary embodiment, the charging unit further includes a firstswitch and a second switch;

The current source, the first switch, the capacitor circuit and thesecond switch are connected in series;

The first terminal of the second switch is connected to the low voltageend of the capacitor, and the second terminal of the second switch isgrounded;

When the capacitor is charged, the current source, the first switch, thecapacitor circuit and the second switch form a current path.

In another exemplary embodiment, the current source may be a voltagesource with a current limiting function, and the output value of thevoltage source is equal to the predetermined voltage of the capacitor.

In an exemplary embodiment, the drive circuit further includes a poweramplifying unit and a control unit;

The power amplifying unit is used to amplify the pulse signal receivedby the drive circuit and output it;

The control unit is used for turning off the power switch through aclamping circuit when the power supply voltage is lower than a firstpredetermined voltage and/or the voltage of the capacitor is lower thana second predetermined voltage.

In an exemplary embodiment, the drive circuit satisfies at least one ofthe following conditions:

When the power switch is a bipolar transistor, the first electrode isthe base, and the second electrode is the emitter; when the power switchis a field effect transistor, the first electrode is the gate, and thesecond electrode is the source;

The power switch is a silicon carbide, silicon or gallium nitride fieldeffect transistor;

The over-voltage adjustment element includes a Zener diode.

The embodiment of the present invention also discloses a drive devicefor a power switch. The drive device includes the drive circuitdisclosed above and a capacitor circuit connected to the output terminalof the drive circuit.

The embodiment of the present invention also discloses a drive devicefor a power switch. The drive device includes the drive circuitdisclosed above, a capacitor circuit connected to the output terminal ofthe drive circuit, and a pulse circuit generating a pulse signal.

The embodiment of the present invention also discloses a drive devicefor a power switch, which includes a second resistor, a capacitor and anegative voltage charge pump;

The second resistor is connected in series with the capacitor. The highvoltage end of the capacitor is connected to the first terminal of thesecond resistor, and the low voltage end of the capacitor is connectedto the first electrode of the power switch and the first terminal of thenegative voltage charge pump;

The second terminal of the second resistor is connected to the secondterminal of the negative voltage charge pump, and the second terminal ofthe second resistor receives the pulse signal that controls the turningon and off of the power switch;

The second electrode of the power switch is grounded.

In an exemplary embodiment, the drive device further includes a currentsource, a first switch and a second switch;

The current source, the first switch, the second resistor, the capacitorand the second switch are connected in series;

The first terminal of the second switch is connected to the low voltageend of the capacitor, and the second terminal of the second switch isgrounded;

When charging the capacitor, the first switch and the second switchtransition from a turn-off state to a turn-on state. The current source,the first switch, the second resistor, the capacitor and the secondswitch form a current path.

Compared with the prior art, the main differences and effects of theembodiments of the present invention are:

Without additional power supplies, when the pulse signal is a turn-offsignal for a long time (such as an idle time), it can promptlysupplement the loss of stored power due to leakage of the capacitor,thereby providing a stable turn-off negative voltage for the powerswitch.

Furthermore, after the capacitor is charged to the requiredpredetermined voltage, a low-power negative voltage charge pump can beused to charge the capacitor and keep it at the predetermined voltage,thereby saving the circuit area and reducing the circuit cost whilemaintaining the negative voltage for a long time.

Furthermore, when the drive module receives the turn-on signal, thefirst resistor and the diode can charge the capacitor when the capacitorvoltage is lower than the predetermined voltage.

Furthermore, the capacitor can be quickly charged when the drive circuitis started or restarted, effectively avoiding the problems ofexcessively high positive voltage or insufficient negative voltage onthe gate of the power switch. At the same time, grounding the first andsecond electrodes of the power switch simultaneously when the capacitoris charged can ensure that the power switch remains off during thecharging period of the capacitor, thereby improving the capacitorcharging efficiency while ensuring the reliability of the circuit.

Furthermore, the over-voltage adjustment element can clamp the voltageof the capacitor to a predetermined voltage to avoid overcharging.

Furthermore, when the power supply voltage is too low or the capacitorvoltage is too low, the gate or base voltage of the power switch can bepulled down to zero volts through the Miller clamping pin to turn offthe power switch and protect the circuit.

The foregoing has outlined rather broadly the features and technicaladvantages of the present disclosure in order that the detaileddescription of the disclosure that follows may be better understood.Additional features and advantages of the disclosure will be describedhereinafter which form the subject of the claims of the disclosure. Itshould be appreciated by those skilled in the art that the conceptionand specific embodiment disclosed may be readily utilized as a basis formodifying or designing other structures or processes for carrying outthe same purposes of the present disclosure. It should also be realizedby those skilled in the art that such equivalent constructions do notdepart from the spirit and scope of the disclosure as set forth in theappended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the present disclosure, and theadvantages thereof, reference is now made to the following descriptionstaken in conjunction with the accompanying drawings, in which:

FIGS. 1 (a)-(c) are schematic diagrams of the circuit structures of thedrive circuits of the power switch in the prior art;

FIG. 2 is a timing diagram of the gate voltage in FIG. 1(a) as afunction of the PWM signal;

FIG. 3 is a block diagram of a power switch and its drive circuitaccording to an embodiment of the present invention;

FIG. 4 is a block diagram of a capacitance adjustment unit according toan embodiment of the present invention;

FIG. 5 is a schematic diagram of the circuit structure of a power switchand its drive circuit according to an embodiment of the presentinvention; and

FIG. 6 is the simulation result of the gate voltage of the power switchin the circuit shown in FIG. 5.

Corresponding numerals and symbols in the different figures generallyrefer to corresponding parts unless otherwise indicated. The figures aredrawn to clearly illustrate the relevant aspects of the variousembodiments and are not necessarily drawn to scale.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

The making and using of the embodiments of this disclosure are discussedin detail below. It should be appreciated, however, that the conceptsdisclosed herein can be embodied in a wide variety of specific contexts.The specific embodiments discussed are merely illustrative, and do notlimit the scope of the claims.

In the following description, many technical details are provided forthe reader to better understand the application. However, those ofordinary skill in the art can understand that even without thesetechnical details and various changes and modifications based on thefollowing embodiments, the technical solutions required by the claims ofthis application can be implemented.

It can be understood that in the present invention, the low voltage endof the capacitor refers to the end of the capacitor with a lower voltage(such as the negative plate of the capacitor), and correspondingly, thehigh voltage end refers to the end with a higher voltage (such as thepositive plate of the capacitor).

In addition, it can be understood that, in the present invention, thepower switch may be various types of switches, which is not limitedherein. Preferably, the power switch is a silicon carbide, silicon orgallium nitride field effect transistor. When the power switch is abipolar transistor, the first electrode is the base and the secondelectrode is the emitter; when the power switch is a field effecttransistor, the first electrode is the gate and the second electrode isthe source.

In addition, it can be understood that the predetermined voltage in thepresent invention refers to the negative voltage charged in thecapacitor for maintaining the power switch in the off state when thedrive circuit is started or restarted. The capacitor of the presentinvention can be a single capacitor, or a capacitor circuit composed ofmultiple capacitors in parallel and/or in series. It is worth notingthat the voltage of the capacitor of the present invention is muchhigher than the voltage of the parasitic capacitor between the gate andsource (or base and emitter) of the power switch, such as more than tentimes, so as to ensure that when the pulse signal is applied, the powerswitch is controlled to be turned off or on, and the negative voltage onthe capacitor remains basically unchanged.

In addition, it can be understood that in the present invention, bothPWM and pulse signals refer to pulse signals used to control the on andoff of the power switch. This time, the pulse circuit that generates thepulse signal can be an analog controller or a digital controller.

In order to make the objectives, technical solutions and advantages ofthe present invention clearer, the embodiments of the present inventionwill be described in further detail below in conjunction with theaccompanying drawings.

The first embodiment of the present invention relates to a drive circuitof a power switch. FIG. 3 is a block diagram of the drive circuit.

Specifically, as shown in FIG. 3, the input terminal of the drivecircuit receives a pulse signal. The pulse signal includes a turn-onsignal and a turn-off signal for controlling the turn-on and turn-off ofthe power switch; the output terminal of the drive circuit is connectedto the capacitor circuit. The capacitor circuit is used to provide anegative voltage applied to the first electrode of the power switch toturn off the power switch when the pulse signal is a turn-off signal.The drive circuit includes a capacitance adjustment unit, a chargingunit, a power amplification unit, and a control unit.

FIG. 4 is a block diagram of the structure of the capacitance adjustmentunit. As shown in FIG. 4, the capacitance adjustment unit includes anegative voltage adjustment element, a positive voltage adjustmentelement, and an over-voltage adjustment element. The negative voltageadjustment element can charge a capacitor whose voltage is lower than apredetermined voltage when the pulse signal is a turn-off signal. Thecapacitor is included in the capacitor circuit. Preferably, the negativevoltage adjustment element includes a negative voltage charge pump forcharging the capacitor whose voltage is lower than the predeterminedvoltage when the drive circuit receives the turn-off signal. Thepositive voltage adjustment element is used to charge the capacitorwhose voltage is lower than the predetermined voltage when the drivecircuit receives the turn-on signal. The over-voltage adjustment elementis used to clamp the voltage of the capacitor to the predeterminedvoltage when the voltage of the capacitor exceeds the predeterminedvoltage. It can be understood that, in some exemplary embodiments of thepresent invention, the negative voltage charge pump can only charge acapacitor with a voltage lower than the predetermined voltage when thedrive circuit receives a turn-off signal. Alternatively, the negativevoltage charge pump can be set to charge the capacitor whose voltage islower than the predetermined voltage when the drive circuit receives theturn-off signal, or the negative voltage charge pump can be set tocharge the capacitor whose voltage is lower than the predeterminedvoltage when the drive circuit receives the turn-on signal.

The charging unit is used to charge the capacitor when the drive circuitis started. Preferably, in an exemplary embodiment, the charging unitincludes a current source. The current source charges the capacitor whenthe drive circuit is activated. In another exemplary embodiment, thecurrent source may be a voltage source with a current limitation, andthe output voltage of the voltage source is the predetermined voltage ofthe capacitor.

The power amplifying unit is used to amplify the pulse signal receivedby the drive circuit and output it.

The control unit is used to turn off the power switch through theclamping circuit when the power supply voltage is lower than a firstpredetermined voltage and/or the voltage of the capacitor is lower thana second predetermined voltage.

The embodiments above are the blocks of the circuit involved in the coreidea of the present invention. In order to describe the technicalsolution of the present invention in more detail, FIG. 5 shows aschematic diagram of the circuit structure of the drive circuit of thepower switch in an exemplary example. As shown in FIG. 5, the drivecircuit includes a pulse signal input, a power amplifier unit 1, acurrent source 2, an under-voltage monitor UVLO 3 and an under-voltagemonitor UVLO 6, a drive logic 4, an over-voltage adjustment element 5, astart logic unit 7, a second switch K 8, a negative voltage charge pump9, a first resistor Rc, a diode Dc, a second resistor Rg, a capacitorCn, and a first switch Qc. Moreover, in this example, the powertransistor Q3 is an NMOS transistor, and its source is grounded. It canbe understood that the type of power switch applicable to the drivecircuit of the present invention is not limited to this, and may beother types of switches.

In this circuit, the negative voltage charge pump 9, the over-voltageadjustment element 5, the first resistor Rc and the diode Dc form acapacitance adjustment unit. Among them, the negative voltage chargepump 9 is used as a negative voltage adjustment element. The firstresistor Rc and the diode Dc form a positive voltage adjustment element.The over-voltage adjustment element 5 preferably uses a Zener diode. Thecapacitor circuit comprises the capacitor Cn and the second resistor Rg.As shown in FIG. 5, the negative voltage charge pump 9 is connected inparallel with the capacitor Cn. The first terminal of the negativevoltage charge pump 9 is connected to the low voltage end of thecapacitor Cn, and the second terminal of the negative voltage chargepump 9 is connected to the second terminal of the second resistor Rgconnected in series to the capacitor Cn. At the same time, the lowvoltage end of the capacitor Cn is connected to the gate of the powerswitch Q3, and the high voltage end of the capacitor Cn is connected tothe first terminal of the second resistor Rg. The first terminal of thefirst resistor Rc is connected to the low voltage end of the capacitorCn. The second terminal of the first resistor Rc is connected to theanode of the diode Dc. The cathode of the diode Dc is grounded. Theover-voltage adjustment element 5 is connected in parallel with thecapacitor Cn. One terminal of the over-voltage adjustment element 5 isconnected to the low voltage end of the capacitor Cn, and the other endof the over-voltage adjustment element 5 is connected to the second endof the second resistor Rg, which is connected in series with thecapacitor Cn. The second resistor Rg is used to limit the current of thepulse signal amplified by the power amplifying unit.

After receiving the pulse signal for turning off the power switch, ifthe voltage of the capacitor Cn decreases (for example, caused byleakage from a long time idle state or other interference factors), thenegative voltage charge pump 9 can charge the capacitor Cn.

When the drive module receives the pulse signal that turns on the powerswitch, the first resistor Re and the diode Dc can charge the capacitor.In other embodiments of the present invention, other existing circuitscan also be used to charge the capacitor when the pulse signal is at ahigh level (that is, the pulse signal for turning on the power switch),which is not limited herein.

The over-voltage adjustment element 5 is used to reduce the voltage ofthe capacitor to the predetermined voltage when the voltage of thecapacitor exceeds the predetermined voltage. Preferably, theover-voltage adjustment element includes a Zener diode. The over-voltageadjustment element can reduce the excessive charging current when thecapacitor is charging.

In the circuit shown in FIG. 5, the current source 2, the first switchQc, and the second switch K form a charging unit. The charging unit isused to charge the capacitor Cn with a current source included in thecharging unit when the drive circuit is started, and when the chargingunit charges Cn, the low voltage end of Cn and the source of Q3 are bothgrounded. The charging unit can quickly charge Cn when the drive circuitis started or restarted. In addition, since the capacitance adjustmentunit can maintain the voltage of Cn, it can maintain the negativevoltage required for the power switch to turn off without requiring anadditional voltage source. At the same time, when Cn is charging, thegate and source of Q3 are grounded at the same time to ensure that Q3remains off during the time of charging Cn, thereby improving thecharging efficiency of Cn while ensuring the reliability of the circuit.Specifically, the current source 2, the first switch Qc, the secondresistor Rg, the capacitor Cn, and the second switch K are sequentiallyconnected in series. The first terminal of the second switch K isconnected to the low voltage end of Cn, and the second terminal of thesecond switch K is grounded. When charging Cn, the first switch Qc andthe second switch K are turned on, and the current source 2, the firstswitch Qc, the second resistor Rg, the capacitor Cn and the secondswitch K form a current path. This helps to achieve fast charging of thecapacitor Cn.

In other embodiments of the present invention, other charging units mayalso be used to charge the capacitor Cn. For example, a charging unitincluding a voltage source can be used. The embodiments are not limitedherein.

When the drive circuit is started or restarted, after the capacitor hasbeen charged to the required predetermined voltage, a low-power negativevoltage charge pump can be used to charge the capacitor in which leakageoccurs. The low-power negative voltage charge pump helps to maintain thevoltage of the capacitor at the predetermined voltage, therebymaintaining the negative voltage for a long time. At the same time, thismethod saves the circuit area and reduces the circuit cost. In addition,in other examples of the present invention, other existing chargingcircuits can also be used to charge Cn, which is not limited herein.

In addition, in the circuit shown in FIG. 5, the power amplifier unit 1is used to achieve the power amplifying function. The power amplifierunit 1 is respectively connected to the drive logic 4 and the secondresistor Rg. The power amplifier unit 1 is used to amplify the pulsesignal received from the drive logic 4 and output it to the secondresistor Rg, thereby controlling the on and off of Q3.

In the circuit shown in FIG. 5, the under-voltage monitor UVLO 3, theunder-voltage monitor UVLO 6, the drive logic 4 and the start logic unit7 form a control unit. The control unit is used for turning off thepower switch through a clamping circuit when the power supply voltage islower than a first predetermined voltage and/or the voltage of thecapacitor circuit is lower than a second predetermined voltage. Itshould be understood that the second predetermined voltage here is muchsmaller than the predetermined voltage of the capacitor, such as thecase where the capacitor circuit is short-circuited. Specifically, theunder-voltage monitors 3 and 6 are connected to the drive logic 4 andthe start logic unit 7. When the under-voltage monitors 3 and 6 detectthat the power supply voltage VDD is lower than the first predeterminedvoltage and/or the voltage Vcn of the capacitor Cn is lower than thesecond predetermined voltage, the start logic unit 2 will output asignal to the drive logic 4. The drive logic 4 reduces the gate voltageof Q3 to zero by controlling the Miller clamp pin (e.g., the clampcircuit), thereby turning off O3, which plays a role in circuitprotection.

In addition, the control unit is also used to control the on and off ofthe first switch Qc and the second switch K in the above-mentionedcharging unit to control whether the capacitor Cn is charged.

It can be understood that the control unit can also use other devices toimplement its functions based on the prior art, which is not limitedherein. In addition, in other embodiments of the present invention,other circuits can also be used to achieve the same function of thenegative voltage pump here, which is not limited herein.

The operating principle of the circuit shown in FIG. 5 is as follows:

When the drive circuit is started or restarted, the capacitor Cn doesnot store charge. The control unit will control the first switch Qc andthe second switch K transitioning from a turn-off state to a turn-onstate. The current source 2, the first switch Qc, the second resistorRg, the capacitor Cn and the second switch K form a current path toquickly charge the capacitor Cn. At the same time, the source and gateof Q3 are both grounded, and Q3 is cut off. During this period, if thecharging voltage of Cn exceeds a predetermined voltage value, theover-voltage adjustment element will clamp it.

After the capacitor has been charged, when the pulse signal is a turn-onsignal, the high-level turn-on signal is amplified by the poweramplifying unit. The voltage at the high voltage terminal of Cn rises,and Q3 is turned on. During this period, if Cn leaks, the circuitcomprising Re and Dc can charge Cn which has a reduced voltage, and ifthe charging voltage of Cn exceeds the predetermined value, theover-voltage adjustment element will clamp it.

When the pulse signal module outputs a low-level turn-off signal such aszero volts, Cn provides a negative voltage to the gate of Q3, so that Q3is turned off. During this period, if Cn leaks or other conditions causethe voltage of Cn to decrease, the negative voltage charge pump 9 willcharge it.

In the above process, if the Cn voltage or VDD is extremely reduced(such as zero volts) caused by a short circuit of Cn or other reasons,the start logic unit 7 will output a signal to the drive logic 4, whichwill control Q3. The gate voltage of Q3 is reduced to zero for achievingcircuit protection.

FIG. 6 shows the simulation result of the circuit shown in FIG. 5. Ascan be seen from FIG. 6, when the capacitor leaks, the negative voltageat the gate of Q3 is maintained, that is, the voltage is maintained atthe predetermined voltage. When an under-voltage condition occurs (thatis, VDD or Vcn is severely reduced), Vg is pulled down to the groundvoltage.

The invention does not require an additional power source, and cantimely supplement the voltage loss caused by leakage or slightinterference to the capacitor when the pulse signal is a turn-off signalfor a long time, such as an idle time, so as to provide a stableturn-off negative voltage for the power switch.

In practical applications, the above-mentioned drive circuit may be aseparate integrated circuit or a non-integrated circuit, which is notlimited herein.

It can be understood that in other exemplary embodiments of the presentinvention, the circuit shown in FIG. 5 may not include the firstresistor Re and the diode Dc, and the negative voltage charge pump 9charges the capacitor Cn when the pulse signal is an on signal.

The second embodiment of the present invention relates to a drive deviceincluding the drive circuit of the first embodiment and the capacitorcircuit.

The third embodiment of the present invention relates to a drive deviceincluding the drive circuit of the first embodiment, a capacitorcircuit, and a pulse circuit that generates a pulse signal.

It should be noted that in the claims and specification of this patent,relational terms such as first and second are only used to distinguishone entity or operation from another entity or operation, and do notnecessarily require or imply that there is any such actual relationshipor order between these entities or operations. Moreover, the terms“include”, “comprise” or any other variants thereof are intended tocover non-exclusive inclusion, so that a process, method, article, ordevice including a series of elements. It includes not only thoseelements, but also includes other elements. It also includes elementsinherent to this process, method, article or equipment. If there are nomore restrictions, the element defined by the phrase “comprising one”does not exclude the existence of other same elements in the process,method, article, or equipment including the element.

Although the present invention has been illustrated and described byreferring to certain preferred embodiments of the present invention,those of ordinary skill in the art should understand that variouschanges can be made in form and details without departing from thespirit and scope of the present invention.

Although embodiments of the present disclosure have been described indetail, it should be understood that various changes, substitutions andalterations can be made herein without departing from the spirit andscope of the disclosure as defined by the appended claims.

Moreover, the scope of the present disclosure is not intended to belimited to the particular embodiments described here. As one of ordinaryskill in the art will readily appreciate from the disclosure of thepresent disclosure that processes, machines, manufacture, compositionsof matter, means, methods, or steps, presently existing or later to bedeveloped, may perform substantially the same function or achievesubstantially the same result as the corresponding embodiments describedherein. Accordingly, the appended claims are intended to include withintheir scope such processes, machines, manufacture, compositions ofmatter, means, methods, or steps.

What is claimed is:
 1. An apparatus comprising: a power switch; acapacitor circuit coupled between an amplifier and a gate of the powerswitch; and a negative voltage adjustment element connected in parallelwith the capacitor circuit, wherein the negative voltage adjustmentelement is configured such that after a turn-off signal is applied tothe gate of the power switch through the amplifier and the capacitorcircuit, a capacitor of the capacitor circuit is charged by the negativevoltage adjustment element, and as a result of charging the capacitor, avoltage of the capacitor is maintained at a predetermined voltage level.2. The apparatus of claim 1, wherein: the negative voltage adjustmentelement is a negative voltage charge pump; and the capacitor circuitcomprises a gate drive resistor and the capacitor connected in series.3. The apparatus of claim 1, wherein: the power switch is selected fromthe group consisting of a silicon carbide (SiC) metal oxidesemiconductor field effect transistor (MOSFET), a silicon MOSFET or aninsulated-gate bipolar transistor (IGBT).
 4. The apparatus of claim 1,further comprising: a startup charging circuit configured to charge thecapacitor during a startup process of the apparatus, wherein after thestartup process finishes, the negative voltage adjustment element isconfigured to charge the capacitor.
 5. The apparatus of claim 4,wherein: the startup charging circuit comprises a current source, afirst switch and a second switch, and wherein the first switch, thecapacitor circuit and the second switch are connected in series betweenthe current source and ground.
 6. The apparatus of claim 5, wherein:during the startup process of the apparatus, the current source isconfigured to charge the capacitor; and during the startup process ofthe apparatus, the gate and a source of the power switch are connectedto a same voltage potential.
 7. The apparatus of claim 1, furthercomprising: an over-voltage adjustment element connected in parallelwith the capacitor circuit, wherein the over-voltage adjustment elementis configured to clamp the voltage of the capacitor to a predeterminedvoltage value when the voltage of the capacitor exceeds thepredetermined voltage value.
 8. The apparatus of claim 1, wherein: thecapacitor circuit is configured to provide a negative voltage applied tothe gate of the power switch after a turn-off signal is fed into theamplifier.
 9. The apparatus of claim 1, further comprising: a positivevoltage adjustment element coupled between the gate of the power switchand ground, wherein the positive voltage adjustment element isconfigured such that after a turn-on signal is applied to the gate ofthe power switch through the amplifier and the capacitor circuit, thecapacitor of the capacitor circuit is charged by the positive voltageadjustment element.
 10. The apparatus of claim 9, wherein: the positivevoltage adjustment element comprises a resistor and a diode connected inseries between the gate of the power switch and ground.
 11. A methodcomprising: during a startup process of a driver of a power switch,charging a capacitor using a first charging circuit, wherein thecapacitor is coupled between the driver and a control terminal of thepower switch; and after the startup process of the driver finishes,charging the capacitor using a negative voltage adjustment element,wherein the capacitor is configured to provide a negative voltage forthe control terminal of the power switch after a turn-off signal is fedinto the driver.
 12. The method of claim 11, further comprising:charging the capacitor using a positive voltage adjustment element aftera turn-on signal is fed into the driver, wherein the positive voltageadjustment element comprises a resistor and diode connected in seriousbetween the control terminal of the power switch and ground.
 13. Themethod of claim 11, further comprising: clamping a voltage of thecapacitor to a predetermined voltage through an over-voltage adjustmentelement coupled in parallel with the capacitor.
 14. The method of claim11, wherein: the first charging circuit comprises a current source, afirst switch and a second switch, and wherein the first switch, thecapacitor and the second switch are coupled in series between thecurrent source and ground.
 15. The method of claim 11, furthercomprising: detecting a first voltage level of a power supply providingpower for the driver; detecting a second voltage level across thecapacitor; and turning off the power switch after the first voltagelevel is less than a predetermined power supply voltage and/or thesecond voltage level is less than a predetermined capacitor voltage. 16.A system comprising: a power switch; a capacitor circuit coupled to acontrol terminal of the power switch; an amplifier configured to receivea pulse signal and generate an amplified signal applied to the controlterminal of the power switch through the capacitor circuit; a negativevoltage adjustment element connected in parallel with the capacitorcircuit; and a startup capacitor charging circuit configured to charge acapacitor of the capacitor circuit during a startup process of thesystem.
 17. The system of claim 16, wherein: the negative voltageadjustment element is configured such that after a turn-off signal isapplied to the control terminal of the power switch through theamplifier and the capacitor circuit, the capacitor of the capacitorcircuit is charged by the negative voltage adjustment element, and as aresult of charging the capacitor, a voltage of the capacitor ismaintained at a predetermined voltage level, and a negative voltage isapplied to the control terminal of the power switch.
 18. The system ofclaim 16, further comprising: a positive voltage adjustment elementcoupled between the control terminal of the power switch and ground,wherein the positive voltage adjustment element is configured such thatafter a turn-on signal is applied to the control terminal of the powerswitch through the amplifier and the capacitor circuit, the capacitor ofthe capacitor circuit is charged by the positive voltage adjustmentelement.
 19. The system of claim 16, further comprising: an over-voltageadjustment element connected in parallel with the capacitor circuit,wherein the over-voltage adjustment element is configured to clamp avoltage of the capacitor to a predetermined voltage value when thevoltage of the capacitor exceeds the predetermined voltage value. 20.The system of claim 16, wherein: the capacitor circuit comprises aresistor and the capacitor connected in series between an output of theamplifier and the control terminal of the power switch, and wherein thecontrol terminal is a gate, and the power switch is a SiC transistor.